1.Technical Field
The present invention relates to an X-ray optical system of a computerized tomographic (CT) apparatus. It particularly relates to the CT apparatus equipped with a mechanism which adjusts a focal point position of an X-ray tube.
2. Background Art
In general, when an X-ray tube for an X-ray computerized tomographic (CT) apparatus is replaced with a new tube, alignment in both lateral and longitudinal directions is needed in order to adjust a focal spot position of the X-ray tube. Referring to FIG. 1, an X-ray tube 101 is mounted to a plate 102 which is used for alignment in the lateral direction. The alignment plate 102 is attached to a plate 103 which is used for alignment in the longitudinal direction. In the plates 102, 103, there is provided respectively a guide rail 104 along which the alignment plates 102, 103 are moved so as to to align the focal spot position of the X-ray tube, by manually operating a fine-adjustment member 105.
Then, an amount to be finely adjusted in the lateral direction is obtained by an X-ray amount profile in a channel direction when a pin-phantom is scanned. The phantom is supported by a pin-shaped material and is positioned in a rotation center of the CT apparatus The finely adjusted amount in the longitudinal direction is obtained by a profile of the X-ray data in a slice thickness direction. Then, a tool having a slit therein, which is movable in the longitudinal direction is mounted to and in front of an X-ray detector.
As described above, after the alignment of the focal spot position in both lateral and longitudinal positions are made, the position of the X-ray tube is fixed.
However, in the event that the alignment of the X-ray tube focal spot position Is manually carried out, a service attendant for the alignment has to go through difficult and cumbersome task for positioning the focal spot.
Moreover, when the focal spot position is moved due to some reasons such as a thermal expansion of a target or anode in the X-ray tube, there occurs a ring like image artifact accompanied by the movement of the focal spot position. However, it is not easy to correct the focal spot position once the X-ray tube position is fixed, so that the image artifact caused thereby has been a troublesome factor.
Moreover, a slit that controls the X-ray amount is moved in the conventional practice, as described in a U.S. Pat. No. 4,991,189 granted to Boomgaarden et al. of General Electric Company on Feb. 5, 1991. As a result, a desired slice position and an X-ray path moved according to movement of the focal spot position can not coincide. Consequently, a spatial resolution and so on thus obtained are greatly deteriorated when a helical scanning operation is performed.